1. Field of the Invention
The present invention relates to an image fixing device for fixing a toner image on recording paper,the fixing device adapted for use in an image forming apparatus such as a copier, a printer, a facsimile transceiver or similar photographic image forming apparatus. More particularly, the invention is concerned with a fixing temperature control device for controlling the fixing temperature to obtain a good fixing condition.
2. Description of the Related Art
In the image forming apparatus which has a plurality of paper feed devices, the distances from the respective paper feed devices to the fixing device differ. Japanese Patent Laid-Open Publication No. 64-40955 discloses an image fixing device in which a reload temperature which can start the paper feed and is lower than the fixing temperature is varied for each paper feed device in consideration of time for feeding the paper from the paper feed device to the fixing device. In this prior art, the reload temperature is set according to the distance from the paper feed device to the fixing device. The temperature between fixing operation at the fixing device is maintained lower when the paper feed distance is longer. As a result the time from operation of a print key until printing is completed is longer and power consumption is reduced.
As another prior art, Japanese Laid-Open publication No. 60-169876 discloses a fixing device for an image forming apparatus in which the fixing temperature is varied according to the thickness of the paper. The apparatus has two modes, one is a cassette mode in which the paper is fed from a paper feed cassette, and the other is a manual mode in which it is fed from a manual paper feed tray. The fixing temperature of the manual mode is higher than that of the cassette mode, taking into consideration the various kinds of paper which are fed from the manual paper feed tray. The fixing temperature in the manual mode, however, is uniformly higher than that in the cassette mode. Therefore, the fixing temperature is low, even if a paper feed path and a paper feed form in the cassette mode are suitable for thick paper and the paper is set in the cassette. As a result, a fixing ability is bad, so that the toner image on the recording paper is bad in quality.